This invention relates to a portable demagnetizer, and more particularly to a demagnetizer unit particularly useful for demagnetizing a lap plate on a lapping machine or for demagnetizing punches and dies in all kinds of presses.
The invention is particularly useful in those instances where it is desired to demagnetize substances or materials which are so large and cumbersome that it is difficult and expensive to move. The principle of demagnetization is well known, and sufficient to state for the purpose of this invention that methods of demagnetization are also well known, but it is not believed to be known to provide a portable demagnetizer of sufficient strength to demagnetize the lap plate of a lapping machine.
The lap plate of a lapping machine as a result of its contact with ferromagnetic material during use as well as a result of friction between the parts to be lapped and the lap plate becomes magnetized, and as a result problems arise in the use of the lapping machine. Specifically, as a result of the magnetization of the lap plate, it becomes possible for small foreign particles to become trapped between the lap plate and work piece so that problems arise in connection with the dimensional tolerances of the work pieces, particularly, if such tolerances are critical. Heretofore, the lap plate would have to be removed from the machine and brought to a stationary demagnetizer and thereby result in delays as well as down time for the lapping machine, as well as a loss due to labor costs. Accordingly, the plate is not demagnetized as often as it should be. The same problem applies to the breakage of punches and dies in a press and to other machines which are not demagnetized as often as they should be.
The prior art is basically the non-portable demagnetizers which have been used and which require the article or element which is to be demagnetized to be brought to it. In general, it is known to the prior art to use thermal demagnetization or demagnetization by applying a D.C. field in a direction opposite to the magnetization direction. Another form of demagnetization is to apply an alternating magnetic potential and slowly reduce its amplitude to zero. As the applied potential is reduced in magnitude, the inductor follows an ever-decreasing hysteresis loop until the magnetizing force and the inductor both reach zero. Similar results can be achieved by slowly moving the work piece away from the alternating field. This form of demagnetization has not heretofore been accomplished with a portable device for demagnetizing parts as heavy as lapping plates.